The invention relates to a method for fabricating a reference layer for MRAM memory cells and to an MRAM memory cell having a reference layer fabricated in this way.
As is known, an MRAM arrangement is based on ferromagnetic storage with the aid of the TMR effect (TMR=tunneling magnetoresistance). The accompanying FIG. 1 illustrates a diagrammatic cross section through a known MRAM memory cell that utilizes said TMR effect. The TMR memory cell, comprising a layer stack having a soft-magnetic layer 2, a tunnel oxide layer 3 and a hard-magnetic or reference layer, lies between a bit line 5 and a word line 4, which cross one another. The magnetization direction (arrow) of the hard-magnetic layer 1 is predetermined, while the magnetization direction (double arrow) of the soft-magnetic layer 2 is adjustable by sending corresponding currents I, I′ in different directions through the word line 4 and the bit line 5. These currents enable the magnetization of the soft-magnetic layer 2 to be polarized parallel or antiparallel with respect to the magnetization direction of the hard-magnetic layer 1. The resistance of the layer stack is lower in the case of parallel magnetization of the two layers 1 and 2 than in the case of antiparallel magnetization, which can be evaluated as state “0” and “1”, or vice versa.
Since the net magnetization of the reference layer determines the overall behavior of the MRAM memory cell, it is desirable to make said net magnetization adjustable in a targeted manner during the fabrication of MRAM memory cells.